Solar cell and method for manufacturing the same

ABSTRACT

A solar cell and a method for manufacturing the same are discussed. The solar cell includes a substrate formed of an n-type crystalline semiconductor, an emitter region of a p-type positioned at a first surface of the substrate, a first dielectric layer positioned on a second surface opposite the first surface of the substrate, second dielectric layers respectively positioned on the emitter region and the first dielectric layer, a third dielectric layer positioned on the second dielectric layer that is positioned on the emitter region, a first electrode which is positioned on the first surface of the substrate and is connected to the emitter region, and a second electrode which is positioned on the second surface of the substrate and is connected to the substrate.

This application claims priority to and the benefit of Korean PatentApplication No. 10-2012-0031644 filed in the Korean IntellectualProperty Office on Mar. 28, 2012, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the invention relate to a solar cell and a method formanufacturing the same.

2. Description of the Related Art

Recently, as existing energy sources such as petroleum and coal areexpected to be depleted, interests in alternative energy sources forreplacing the existing energy sources are increasing. Among thealternative energy sources, solar cells for generating electric energyfrom solar energy have been particularly spotlighted.

A solar cell generally includes semiconductor parts, for example, asubstrate and an emitter region, which respectively have differentconductive types, for example, a p-type and an n-type and thus form ap-n junction, and electrodes respectively connected to the semiconductorparts of the different conductive types.

When light is incident on the solar cell, electrons inside thesemiconductor parts become free electrons (hereinafter referred to as‘electrons’) by the photoelectric effect. Further, electrons and holesrespectively move to the n-type semiconductor (e.g., the emitter region)and the p-type semiconductor (e.g., the substrate) under the influenceof the p-n junction of the semiconductor parts. The electrons moving tothe emitter region and the holes moving to the substrate arerespectively collected by the respective electrodes electricallyconnected to the emitter region and the substrate. The electrodes areconnected to each other using electric wires to thereby obtain electricpower.

SUMMARY OF THE INVENTION

In one aspect, there is a solar cell including a substrate formed of ann-type crystalline semiconductor, an emitter region of a p-typepositioned at a first surface of the substrate, a first dielectric layerpositioned on a second surface opposite the first surface of thesubstrate, second dielectric layers respectively positioned on theemitter region and the first dielectric layer, a third dielectric layerpositioned on the second dielectric layer that is positioned on theemitter region, a first electrode which is positioned on the firstsurface of the substrate and is connected to the emitter region, and asecond electrode which is positioned on the second surface of thesubstrate and is connected to the substrate, wherein the emitter regionhas a first textured surface including a plurality of first protrusionseach having a protruding height and a maximum diameter which are withina range of about 5 μm to 10 μm, and wherein each of the plurality offirst protrusions has a second textured surface including a plurality ofsecond protrusions each having a protruding height and a maximumdiameter which are within a range of about 300 nm to 600 nm.

The first dielectric layer and the third dielectric layer may be formedof hydrogenated silicon nitride. The second dielectric layer may beformed of aluminum oxide.

The second dielectric layer may have a thickness of about 5 nm to 15 nm.

Each of the first dielectric layer and the third dielectric layer mayhave a thickness of about 70 nm to 100 nm.

The solar cell may further include a hydrogenated silicon oxide layerpositioned between the first dielectric layer and the third dielectriclayer. The hydrogenated silicon oxide layer may have a thickness ofabout 50 nm to 100 nm.

The solar cell may further include a silicon oxide layer positionedbetween the second surface of the substrate and the first dielectriclayer. The silicon oxide layer may have a thickness of about 2 nm to 3nm.

The first surface and the second surface of the substrate may beincident surfaces on which light is incident.

The solar cell may further include a hydrogenated silicon oxide layerpositioned on the second dielectric layer that is positioned on thefirst dielectric layer. The hydrogenated silicon oxide layer may have athickness of about 50 nm to 100 nm.

The solar cell may further include a silicon oxide layer positionedbetween the emitter region and the second dielectric layer. The siliconoxide layer may have a thickness of about 2 nm to 3 nm.

Acicular ends of the plurality of second protrusions may point in aparallel direction as vertices of the plurality of first protrusions.

Each of the plurality of second protrusions may have an acicular end,and acicular ends of adjacent second protrusions may be connected byserrated edges.

According to the above-described characteristics of the solar cell,because the surface of the substrate has the first and second texturedsurfaces, an amount of light incident on the substrate increases. Hence,the efficiency of the solar cell is improved.

Furthermore, because an anti-reflection layer including the plurality ofdielectric layers and a passivation layer including the plurality ofdielectric layers are respectively formed on a front surface and a backsurface of the substrate, a reflection amount of light decreases. Hence,a surface passivation effect is generated at the surface of thesubstrate, and the efficiency of the solar cell is further improved.

Furthermore, because a field passivation effect is obtained by stackinga layer having negative fixed charges on the n-type substrate, a lossamount of carriers of the solar cell decreases.

In addition, because the problem resulting from a natural oxide layer isreduced by thinly coating the silicon oxide layer on at least one of thefront surface and the back surface of the substrate, the efficiency ofthe solar cell is further improved.

In another aspect, there is a method for manufacturing a solar cellincluding performing a wet etching process to form a first texturedsurface on at least one surface of a substrate, performing a dry etchingprocess to form a second textured surface on the first textured surface,and performing an ion implantation process to implant impurity ions intothe first textured surface and the second textured surface andperforming an activation process to form at least one of an emitterregion and a back surface field region.

The wet etching process may be performed using an alkali solution suchas isopropyl alcohol (IPA) or potassium hydroxide (KOH).

The first textured surface including a plurality of first protrusionsand a plurality of first depressions may be formed through the wetetching process using the alkali solution. A protruding height and adiameter of each of the plurality of first protrusions may be within therange of about 5 μm to 10 μm.

The dry etching process may be performed using a reaction ion etching(RIE) method.

The second textured surface including a plurality of second protrusionsand a plurality of second depressions may be formed through the dryetching process using the reaction ion etching method. A protrudingheight and a diameter of each of the plurality of second protrusions maybe within the range of about 300 nm to 600 nm.

The method may further include, after forming the second texturedsurface, performing the dry etching process to remove a remainder of thesubstrate.

The first and second textured surfaces may be formed on a first surfaceof the substrate, and the first and second textured surfaces are formedon a second surface opposite the first surface. In this instance, theemitter region may be formed at the first surface of the substrate, andthe back surface field region may be locally formed at the secondsurface of the substrate.

In the embodiment of the invention, the local formation of the backsurface field region indicates that the back surface field region isformed in the same pattern as the plurality of finger electrodes of thesecond electrode part at the second surface of the substrate.

Accordingly, the back surface field region is locally formed at thesecond surface of the substrate, unlike the emitter region entirelyformed at the first surface of the substrate.

In the embodiment of the invention, the formation of the emitter regionat the entire first surface of the substrate indicates that the emitterregion is formed at the entire first surface of the substrate except anedge.

The emitter region may be formed by implanting and activating firstimpurity ions, and the back surface field region may be formed byimplanting and activating second impurity ions of a conductive typeopposite the first impurity ions. An activation process of the firstimpurity ions and the second impurity ions may be performed at atemperature of about 1,000° C. to 2,000° C. capable of activating thefirst impurity ions for about 20 minutes to 60 minutes.

The method may further include performing the activation process toremove damaged portions of the first and second surfaces of thesubstrate resulting from the dry etching process.

The method may further include forming a first dielectric layer on thesecond surface of the substrate, simultaneously forming seconddielectric layers respectively on the emitter region and the firstdielectric layer, forming a third dielectric layer on the seconddielectric layer that is positioned on the emitter region, and forming afirst electrode part, which includes a plurality of finger electrodesand is connected to the emitter region, and a second electrode part,which includes a plurality of finger electrodes and is connected to theback surface field region.

At least one of the first electrode part and the second electrode partmay include at least one bus electrode extending in a direction crossingthe finger electrodes.

Each of the first dielectric layer and the third dielectric layer may beformed by depositing hydrogenated silicon nitride at a thickness ofabout 70 nm to 100 nm. The second dielectric layer may be formed bydepositing aluminum oxide at a thickness of about 5 nm to 15 nm using anatomic layer deposition (ALD) method.

The method may further include forming a fourth dielectric layer betweenthe first dielectric layer and the second dielectric layer and on thethird dielectric layer. The fourth dielectric layer may be formed bydepositing hydrogenated silicon oxide at a thickness of about 50 nm to100 nm.

The method may further include, before forming the first dielectriclayer, forming a fifth dielectric layer on the first and second surfacesof the substrate. The forming of the fifth dielectric layer may includeimmersing the substrate in a nitric acid solution having a hydrogen ionconcentration (pH) of about 2 to 4 for about 5 minutes to 30 minutes toform a silicon oxide layer having a thickness of about 2 nm to 3 nm.

The back surface field region may be formed in the same pattern as theplurality of finger electrodes of the second electrode part.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a partial perspective view of a solar cell according to anexample embodiment of the invention;

FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1;

FIG. 3 illustrates a portion of a substrate of the solar cell shown inFIGS. 1 and 2, on which a wet etching process and a dry etching processare performed;

FIGS. 4A to 4H sequentially illustrate a method for manufacturing asolar cell according to an example embodiment of the invention;

FIG. 5 is a partial cross-sectional view of another example of a solarcell according to an example embodiment of the invention; and

FIGS. 6 and 7 are partial cross-sectional views of other examples of asolar cell according to an example embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to embodiments of the invention,examples of which are illustrated in the accompanying drawings. Thisinvention may, however, be embodied in many different forms and shouldnot be construed as limited to the embodiments set forth herein.Wherever possible, the same reference numbers will be used throughoutthe drawings to refer to the same or like parts. It will be paidattention that detailed description of known arts will be omitted if itis determined that the arts can mislead the embodiments of theinvention.

In the drawings, the thickness of layers, films, panels, regions, etc.,are exaggerated for clarity. It will be understood that when an elementsuch as a layer, film, region, or substrate is referred to as being “on”another element, it can be directly on the other element or interveningelements may also be present. In contrast, when an element is referredto as being “directly on” another element, there are no interveningelements present.

Further, it will be understood that when an element such as a layer,film, region, or substrate is referred to as being “entirely” on otherelement, it may be on the entire surface of the other element and maynot be on a portion of an edge of the other element.

Example embodiments of the invention will be described in detail withreference to FIGS. 1 to 7.

A solar cell according to an example embodiment of the invention isdescribed in detail with reference to FIGS. 1 and 2.

As shown in FIGS. 1 and 2, a solar cell according to an exampleembodiment of the invention includes a substrate 110, an emitter region121 positioned at a front surface (or a first surface) of the substrate110, an anti-reflection layer 130 positioned on the emitter region 121,a passivation layer 190 positioned on a back surface (or a secondsurface) opposite the front surface of the substrate 110, a frontelectrode part (or a first electrode part) 140 which is positioned onthe front surface of the substrate 110, is connected to the emitterregion 121, and includes a plurality of front electrodes (or a pluralityof first electrodes) 141 and a plurality of front bus bars (or aplurality of first bus bars) 142, a back electrode part (or a secondelectrode part) 150 which is positioned on the back surface of thesubstrate 110 and includes a plurality of back electrodes (or aplurality of second electrodes) 151 and a plurality of back bus bars (ora plurality of second bus bars) 152, and a plurality of back surfacefield regions 172 positioned under the plurality of back electrodes 151and the plurality of back bus bars 152 at the back surface of thesubstrate 110.

In the embodiment of the invention, light is incident on at least one ofthe front surface and the back surface of the substrate 110.

The substrate 110 is a semiconductor substrate formed of a semiconductorsuch as first conductive type silicon, for example, n-type silicon,though not required. The semiconductor used in the substrate 110 is acrystalline semiconductor, such as single crystal silicon andpolycrystalline silicon. The n-type substrate 110 is doped withimpurities of a group V element such as phosphorus (P), arsenic (As),and antimony (Sb).

As shown in FIGS. 1 to 3, a separate texturing process is entirelyperformed on the flat front surface of the substrate 110 to form a firsttextured surface corresponding to an uneven surface or having unevencharacteristics, and including a plurality of first protrusions 11 and aplurality of first depressions 12. In this instance, the emitter region121 and the anti-reflection layer 130 positioned on the front surface ofthe substrate 110 have the textured surface.

Each of the first protrusions 11 has a pyramid shape or a similar shape.

In the embodiment of the invention, a diameter (i.e., size) ‘a’ and aprotruding height ‘b’ of each of the first protrusions 11 may be withinthe range of several μm, for example, about 5 μm to 10 μm. An aspectratio ‘b/a’ of each first protrusion 11 may be about 1.0 to 1.5. In theembodiment of the invention, the aspect ratio ‘b/a’ is obtained bydividing the protruding height ‘b’ of the first protrusion 11 by thediameter ‘a’ of the first protrusion 11. The diameter ‘a’ of the firstprotrusion 11 is a width of the base of the first protrusion 11.

Because the plurality of first protrusions 11 are positioned on thefront surface of the substrate 110, an incident area of the substrate110 increases and a light reflectance decreases due to a plurality ofreflection operations resulting from each first protrusion 11. Hence, anamount of light incident on the substrate 110 increases, and theefficiency of the solar cell is improved.

As shown in FIGS. 2 and 3, a plurality of second protrusions 111 and aplurality of second depressions 112 are formed on the surface of eachfirst protrusion 11. Thus, the surface of each first protrusion 11 has asecond textured surface corresponding to an uneven surface or havinguneven characteristics, and including the plurality of secondprotrusions 111 and the plurality of second depressions 112.

A diameter (i.e., size) and a protruding height of each of the secondprotrusions 111 included in each first protrusion 11 are less than thediameter (i.e., size) and the protruding height of each first protrusion11.

For example, the diameter and the protruding height of each secondprotrusion 111 may be within the range of several hundreds of nm. Forexample, each second protrusion 111 may have the maximum diameter andthe protruding height of about 300 nm to 600 nm.

Because the surface of each first protrusion 11 has the second texturedsurface, the incident area of the substrate 110 further increases.Further, because a reflection operation of light is repeatedlyperformed, an amount of light incident on the substrate 110 furtherincreases.

As described above, the surface of the substrate 110 forms the firsttextured surface having the first protrusions 11 and the firstdepressions 12, and the surface of each first protrusion 11 forms thesecond textured surface having the second protrusions 111 and the seconddepressions 112. Namely, the surface of the substrate 110 has the firstand second textured surfaces. Thus, a reflectance (for example, anaverage weighted reflectance) of light having a wavelength of about 300nm to 1,100 nm has a small value of about 1% to 10%.

As shown in FIGS. 2 and 3, the first protrusions 11 have a plurality ofsurfaces that meet at respective vertices that are generally piked. Eachof the plurality of surfaces of the first protrusions 11 has a pluralityof second protrusions 111 that have acicular ends. Each of the secondprotrusions 111 are connected to other second protrusions 111 byserrated edges that defined the plurality of depressions 112. Theplurality of second protrusions 111 generally point in a paralleldirection as the vertices of the plurality of first protrusions 11. Theplurality of depressions 112 are also generally hollowed out in theparallel direction as the vertices of the plurality of first protrusions11.

In the embodiment of the invention, when the substrate 110 is formed ofsingle crystal silicon, the first textured surface 11(12) may be formedthrough a wet etching method using an alkali solution such as isopropylalcohol (IPA) or potassium hydroxide (KOH), and the second texturedsurface 111(112) may be formed through a dry etching method such as areaction ion etching (RIE) method.

The emitter region 121 positioned at the front surface of the substrate110 is an impurity region doped with impurities of a second conductivetype (for example, p-type) opposite the first conductive type (forexample, n-type) of the substrate 110. Thus, the emitter region 121 ofthe second conductive type forms a p-n junction along with a firstconductive type region (for example, an n-type region) of the substrate110.

In the embodiment of the invention, the emitter region 121 may have asheet resistance of about 70 Ω/sq. to 80 Ω/sq.

Regarding carriers, for example, electrons and holes produced by lightincident on the substrate 110, the electrons and the holes respectivelymove to the n-type semiconductor and the p-type semiconductor by abuilt-in potential difference resulting from the p-n junction betweenthe substrate 110 and the emitter region 121. Thus, when the substrate110 is of the n-type and the emitter region 121 is of the p-type, theelectrons and the holes move to the substrate 110 and the emitter region121, respectively.

When the emitter region 121 is of the p-type, the emitter region 121 maybe formed by doping the substrate 110 with impurities of a group IIIelement such as boron (B), gallium (Ga), and indium (In). In thisinstance, the emitter region 121 may be formed using an ion implantationmethod.

The anti-reflection layer 130 includes a first anti-reflection layer 131positioned on the emitter region 121 and a second anti-reflection layer132 positioned on the first anti-reflection layer 131.

In the embodiment of the invention, the first anti-reflection layer 131may be formed of aluminum oxide (Al₂O₃), and the second anti-reflectionlayer 132 may be formed of hydrogenated silicon nitride (SiNx:H).

The first anti-reflection layer 131 formed of aluminum oxide (Al₂O₃) mayhave a thickness of about 5 nm to 15 nm and a refractive index of about1.1 to 1.6. The second anti-reflection layer 132 formed of hydrogenatedsilicon nitride (SiNx:H) may have a thickness of about 70 nm to 100 nmand a refractive index of about 2.0 to 2.2.

In this instance, because the refractive index of the firstanti-reflection layer 131 adjacent to the substrate 110 is less than therefractive index of the second anti-reflection layer 132 adjacent toair, an anti-reflection effect is reduced by the refractive index of thefirst anti-reflection layer 131. It is preferable, but not required,that the thickness of the first anti-reflection layer 131 is much lessthan the thickness of the second anti-reflection layer 132, so as toprevent a reduction in the anti-reflection effect.

The first anti-reflection layer 131 formed of aluminum oxide (Al₂O₃) ispositioned on the front surface of the substrate 110, i.e., directly onthe emitter region 121 positioned at the front surface of the substrate110.

In general, aluminum oxide (Al₂O₃) has the characteristic of negativefixed charges.

Thus, positive fixed charges (i.e., holes) are drawn to the p-typeemitter region 121 and electrons are pushed to the back surface of thesubstrate 110 by the first anti-reflection layer 131 formed of aluminumoxide (Al₂O₃) having negative fixed charges. Namely, a field passivationeffect is obtained.

Accordingly, an amount of holes moving to the emitter region 121 furtherincreases by the first anti-reflection layer 131 formed of aluminumoxide (Al₂O₃), and an amount of electrons moving to the emitter region121 decreases by the first anti-reflection layer 131. Hence, arecombination of electrons and holes at and around the emitter region121 is reduced.

Oxygen (O) contained in aluminum oxide (Al₂O₃) for forming the firstanti-reflection layer 131 moves to the surface of the substrate 110abutting on the first anti-reflection layer 131 to thereby perform apassivation function for converting a defect, for example, danglingbonds existing at and around the surface of the substrate 110 intostable bonds.

The first anti-reflection layer 131 formed of aluminum oxide (Al₂O₃) maybe formed using an atomic layer deposition (ALD) method having anexcellent step coverage.

As described above, the first textured surface 11(12) using the wetetching method and the second textured surface 111(112) using the dryetching method are formed on the front surface of the substrate 110.Therefore, a roughness of the front surface (i.e., the surface of theemitter region 121) of the substrate 110 abutting on the firstanti-reflection layer 131 further increases compared to when only thefirst textured surface 11(12) is formed.

If the first anti-reflection layer 131 is formed directly on the emitterregion 121 using a deposition method such as a plasma enhanced chemicalvapor deposition (PECVD) method, the first anti-reflection layer 131 maynot be normally coated on the first and second protrusions 11 and 111and the first and second depressions 12 and 112. Hence, a non-formationarea of the first anti-reflection layer 131 may increase in the firstand second textured surfaces of the substrate 110.

In this instance, a surface passivation effect may be not generated inthe non-formation area of the first anti-reflection layer 131. As aresult, an amount of carriers lost at and around the surface of thesubstrate 110 may increase.

On the other hand, in the embodiment of the invention, the firstanti-reflection layer 131 is formed on the emitter region 121 using theatomic layer deposition method having the excellent step coverage.Therefore, the first anti-reflection layer 131 is normally formed on thefirst and second protrusions 11 and 111 and the first and seconddepressions 12 and 112. Hence, the non-formation area of the firstanti-reflection layer 131 decreases in the first and second texturedsurfaces of the substrate 110.

Accordingly, because a formation area of the first anti-reflection layer131 increases in the first and second textured surfaces of the substrate110, the surface passivation effect using the first anti-reflectionlayer 131 is improved. Hence, an amount of carriers lost at and aroundthe surface of the substrate 110 decreases, and the efficiency of thesolar cell is improved.

The second anti-reflection layer 132 formed of hydrogenated siliconnitride (SiNx:H) is positioned directly on the first anti-reflectionlayer 131 on the front surface of the substrate 110.

Hydrogen (H) contained in hydrogenated silicon nitride (SiNx:H) forforming the second anti-reflection layer 132 moves to the surface of thesubstrate 110 via the first anti-reflection layer 131 to thereby performa passivation function at and around the surface of the substrate 110.

An amount of carriers lost at and around the surface of the substrate110 further decreases by the passivation function using both the firstand second anti-reflection layers 131 and 132.

As described above, because the double-layered anti-reflection layer 130including the first anti-reflection layer 131 formed of aluminum oxide(Al₂O₃) and the second anti-reflection layer 132 formed of hydrogenatedsilicon nitride (SiNx:H) is formed on the front surface of the substrate110, the field passivation effect using the fixed charges of the firstanti-reflection layer 131 and the surface passivation effect using thefirst and second anti-reflection layers 131 and 132 are obtained inaddition to the anti-reflection effect of light using changes in therefractive indexes of the first and second anti-reflection layers 131and 132.

When the thickness of the first anti-reflection layer 131 formed ofaluminum oxide is equal to or greater than about 5 nm, the aluminumoxide layer 131 is more uniformly formed and the field passivationeffect using the fixed charges of the first anti-reflection layer 131 ismore stably obtained. When the thickness of the first anti-reflectionlayer 131 is equal to or less than about 15 nm, manufacturing time andcost of the first anti-reflection layer 131 are reduced without areduction in the anti-reflection effect resulting from the refractiveindex of the first anti-reflection layer 131.

When the thickness of the second anti-reflection layer 132 formed ofhydrogenated silicon nitride is equal to or greater than about 70 nm,the silicon nitride layer 132 is more uniformly formed and the surfacepassivation effect using hydrogen (H) is more stably obtained. When thethickness of the second anti-reflection layer 132 is equal to or lessthan about 100 nm, manufacturing time and cost of the secondanti-reflection layer 132 are reduced without a reduction in the fieldpassivation effect using silicon nitride having positive fixed charges.

Each of the plurality of back surface field regions 172 positioned atthe back surface of the substrate 110 is a region that is more heavilydoped than the substrate 110 with impurities of the same conductive type(for example, the n-type) as the substrate 110.

The back surface field regions 172 abut on the back electrodes 151 andthe back bus bars 152 positioned on the back surface of the substrate110, and are selectively or locally positioned at the back surface ofthe substrate 110.

Hence, the back surface field regions 172 are not positioned between theadjacent back electrodes 151, between the back electrodes 151 and theback bus bars 152, and between the adjacent back bus bars 152.

A potential barrier is formed by a difference between impurityconcentrations of the first conductive type region (for example, then-type region) of the substrate 110 and the back surface field regions172. Hence, the potential barrier prevents or reduces holes from movingto the back surface field regions 172 used as a moving path of electronsand makes it easier for electrons to move to the back surface fieldregions 172.

Thus, the back surface field regions 172 reduce an amount of carrierslost by a recombination and/or a disappearance of the electrons and theholes at and around the back surface of the substrate 110 and acceleratea movement of desired carriers (for example, electrons), therebyincreasing an amount of carriers moving to the back electrode part 150.

Because the impurity concentration of the back surface field regions 172is higher than the impurity concentration of the substrate 110, theconductivity of the back surface field regions 172 abutting on the backelectrode part 150 is greater than the conductivity of the substrate110. Hence, a movement of carriers from the back surface field regions172 to the back electrode part 150 is easily carried out.

The passivation layer 190 includes a first passivation layer 191positioned directly on the back surface of the substrate 110 and asecond passivation layer 192 positioned directly on the firstpassivation layer 191.

The first passivation layer 191 may be formed of hydrogenated siliconnitride (SiNx:H), and the second passivation layer 192 may be formed ofaluminum oxide (Al₂O₃).

In the embodiment of the invention, the first passivation layer 191 andthe second anti-reflection layer 132 may be simultaneously formedthrough the same process, or the second passivation layer 192 and thefirst anti-reflection layer 131 may be simultaneously formed through thesame process.

Hence, the first passivation layer 191 may be formed of the samematerial as the second anti-reflection layer 132 and thus may have thesame characteristics, for example, thickness, properties, component,composition (or composition ratio), refractive index, etc., as thesecond anti-reflection layer 132. Further, the second passivation layer192 may be formed of the same material as the first anti-reflectionlayer 131 and thus may have the same characteristics, for example,thickness, properties, component, composition (or composition ratio),refractive index, etc., as the first anti-reflection layer 131.

More specifically, the first passivation layer 191 formed ofhydrogenated silicon nitride (SiNx:H) may have a thickness of about 70nm to 100 nm and a refractive index of about 2.0 to 2.2. The secondpassivation layer 192 formed of aluminum oxide (Al₂O₃) may have athickness of about 5 nm to 15 nm and a refractive index of about 1.1 to1.6.

Because the first passivation layer 191 formed of hydrogenated siliconnitride (SiNx:H) is positioned on the back surface field regions 172positioned directly on the back surface of the substrate 110, thesurface passivation function using hydrogen (H) is performed. Hence, anamount of carriers lost at and around the back surface of the substrate110 decreases.

Hydrogenated silicon nitride (SiNx:H) has the characteristic of positivefixed charges opposite aluminum oxide (Al₂O₃).

In the embodiment of the invention, the substrate 110 is of the n-type,and the first passivation layer 191, which is formed directly on theback surface of the substrate 110 using silicon nitride, has thecharacteristic of positive fixed charges. Hence, negative charges (i.e.,electrons) moving to the first passivation layer 191 have a polarityopposite the first passivation layer 191 formed of silicon nitride. As aresult, the electrons are drawn to the first passivation layer 191because of the positive polarity of the first passivation layer 191. Onthe other hand, positive charges (i.e., holes) have the same polarity asthe first passivation layer 191 and thus are pushed to the front surfaceof the substrate 110 opposite the first passivation layer 191 because ofthe positive polarity of the first passivation layer 191.

Hence, when the first passivation layer 191 is formed directly on theback surface of the n-type substrate 110 using hydrogenated siliconnitride (SiNx:H), an amount of electrons moving to the back surface ofthe substrate 110 further increases because of the influence of positivefixed charges. Further, the recombination of the electrons and the holesat and around the back surface of the substrate 110 is reduced.

The second passivation layer 192, which is formed on the firstpassivation layer 191 using aluminum oxide (Al₂O₃), prevents hydrogen(H) contained in the first passivation layer 191 from moving to the backelectrode part 150 opposite the front surface of the substrate 110because of heat applied when the solar cell is manufactured. As aresult, the surface passivation effect of the back surface of thesubstrate 110 using hydrogen (H) contained in the first passivationlayer 191 is improved.

As described above, the double-layered passivation layer 190 includingthe first passivation layer 191 formed of hydrogenated silicon nitride(SiNx:H) and the second passivation layer 192 formed of aluminum oxide(Al₂O₃) is formed on the back surface of the substrate 110, in the samemanner as the double-layered anti-reflection layer 130 positioned on thefront surface of the substrate 110. Hence, the surface passivationeffect of the back surface of the substrate 110 is improved.

It is preferable, but not required, that the thickness of the firstpassivation layer 191 is greater than the thickness of the secondpassivation layer 192 positioned on the first passivation layer 191, sothat the second passivation layer 192 having the negative fixed chargesdoes not adversely affect the first passivation layer 191 having thepositive fixed charges. Further, the thickness of the first passivationlayer 191 may be greater than the thickness of the secondanti-reflection layer 132 on the front surface of the substrate 110.

Accordingly, if necessary, the thickness of the hydrogenated siliconnitride layer (i.e., the second anti-reflection layer 132) positioned onthe front surface of the substrate 110 may be different from thethickness of the silicon nitride layer (i.e., the first passivationlayer 191) positioned on the back surface of the substrate 110. In thisinstance, the silicon nitride layer (i.e., the second anti-reflectionlayer 132) positioned on the front surface of the substrate 110 may havethe thickness of about 90 nm, and the silicon nitride layer (i.e., thefirst passivation layer 191) positioned on the back surface of thesubstrate 110 may have the thickness of about 100 nm.

When light is incident on the back surface of the substrate 110, arefractive index in going from air to the substrate 110 increases.Therefore, a reflection amount of light incident on the back surface ofthe substrate 110 decreases, and an amount of light absorbed in thesubstrate 110 increases. Hence, when light is incident on the backsurface of the substrate 110, the passivation layer 190 serves as ananti-reflection layer.

The plurality of front electrodes 141 of the front electrode part 140are connected to the emitter region 121, and the plurality of front busbars 142 of the front electrode part 140 are connected to the frontelectrodes 141 as well as the emitter region 121.

The front electrodes 141 are electrically and physically connected tothe emitter region 121 and are separated from one another. The frontelectrodes 141 extend parallel to one another in a fixed direction. Thefront electrodes 141 collect carriers (for example, holes) moving to theemitter region 121.

The front bus bars 142 are electrically and physically connected to theemitter region 121 and extend parallel to one another in a directioncrossing the front electrodes 141.

The front bus bars 142 have to collect not only carriers (for example,holes) moving from the emitter region 121 but also carriers collected bythe front electrodes 141 crossing the front bus bars 142 and have tomove the collected carriers in a desired direction. Thus, a width ofeach front bus bar 142 may be greater than a width of each frontelectrode 141.

In the embodiment of the invention, the front bus bars 142 arepositioned on the same level layer as the front electrodes 141 and areelectrically and physically connected to the front electrodes 141 atcrossings of the front electrodes 141 and the front bus bars 142.

Accordingly, as shown in FIG. 1, the plurality of front electrodes 141have a stripe shape extending in a transverse (or longitudinal)direction, and the plurality of front bus bars 142 have a stripe shapeextending in a direction crossing the front electrodes 141, for example,in a longitudinal (or transverse) direction. Hence, the front electrodepart 140 has a lattice shape on the front surface of the substrate 110.

The front bus bars 142 are connected to an external device and outputthe collected carriers to the external device.

The front electrode part 140 including the front electrodes 141 and thefront bus bars 142 is formed of at least one conductive material, forexample, silver (Ag).

The plurality of back electrodes 151 of the back electrode part 150 arepositioned on the back surface field regions 172 and directly abut onthe back surface field regions 172. The back electrodes 151 areseparated from one another and extend in a fixed direction in the samemanner as the front electrodes 141. In this instance, the backelectrodes 151 extend in the same direction as the front electrodes 141.The back electrodes 151 collect carriers (for example, electrons) movingto the back surface field regions 172.

The plurality of back bus bars 152 of the back electrode part 150 arepositioned on the back surface field regions 172 and abut on the backsurface field regions 172. The back bus bars 152 extend parallel to oneanother in a direction crossing the back electrodes 151. In thisinstance, the back bus bars 152 extend in the same direction as thefront bus bars 142. The back bus bars 152 may be positioned opposite thefront bus bars 142 with the substrate 110 interposed between them.

The back bus bars 152 collect carriers (for example, electrons)collected by the back electrodes 151 crossing the back bus bars 152 andmove the collected carriers in a desired direction. Thus, a width ofeach back bus bar 152 may be greater than a width of each back electrode151.

The back bus bars 152 are positioned on the same level layer as the backelectrodes 151 and are electrically and physically connected to the backelectrodes 151 at crossings of the back electrodes 151 and the back busbars 152.

Thus, the back electrode part 150 has a lattice shape on the backsurface of the substrate 110 in the same manner as the front electrodepart 140.

The back electrodes 151 and the back bus bars 152 may contain the sameconductive material, for example, silver (Ag) as the front electrodes141 and the front bus bars 142. Alternatively, the back electrode part150 may be formed of a material different from the front electrode part140, and the back electrodes 151 may be formed of a material differentfrom the back bus bars 152.

As described above, in the embodiment of the invention, the back surfacefield regions 172 are positioned under the back electrodes 151 and theback bus bars 152 and extend along the back electrodes 151 and the backbus bars 152. Hence, the back surface field regions 172 are selectivelyor locally positioned at the back surface of the substrate 110 and havea lattice shape in the same manner as the back electrode part 150. Thus,as described above, a non-formation portion of the back surface fieldregions 172 exists at the back surface of the substrate 110.

In the embodiment of the invention, the number of front electrode 141,which are positioned on the front surface of the substrate 110 andreceive the most of light, is less than the number of back electrode151, which are positioned on the back surface of the substrate 110 andreceive a smaller amount of light than the front surface of thesubstrate 110. Thus, a distance between the two adjacent frontelectrodes 141 is greater than a distance between the two adjacent backelectrodes 151.

As described above, because the front electrode part 140 and the backelectrode part 150 contain a metal material such as silver (Ag), thefront electrode part 140 and the back electrode part 150 do not transmitlight.

Because the distance between the front electrodes 141 is greater thanthe distance between the back electrodes 151, a reduction in an incidentarea of light at the front surface of the substrate 110 is reduced orprevented by the arrangement of the front electrodes 141. Hence, anamount of light incident on the front surface of the substrate 110increases.

In another embodiment, the front bus bars 142, the back bus bars 152, orboth may be omitted if needed or desired.

In the embodiment of the invention, at least one of the front electrodepart 140 and the back electrode part 150 may be formed using a platingmethod.

When at least one of the front electrode part 140 and the back electrodepart 150 is formed using the plating method, at least one of the frontelectrode part 140 and the back electrode part 150 may have asingle-layered structure as in the embodiment of the invention.Alternatively, at least one of the front electrode part 140 and the backelectrode part 150 may have a multi-layered structure such as adouble-layered structure and a triple-layered structure. When at leastone of the front electrode part 140 and the back electrode part 150formed using the plating method has the single-layered structure, atleast one of the front electrode part 140 and the back electrode part150 may be formed of silver (Ag).

When at least one of the front electrode part 140 and the back electrodepart 150 formed using the plating method has the double-layeredstructure, a lower layer (or a first layer), which abuts on the emitterregion 121 (i.e., a second conductive type region of the substrate 110)or abuts on the back surface field regions 172 (i.e., a heavily dopedregion of the substrate 110 doped with impurities of the firstconductive type), may be formed of nickel (Ni), and an upper layer (or asecond layer) on the lower layer may be formed of silver (Ag).

When at least one of the front electrode part 140 and the back electrodepart 150 formed using the plating method has the triple-layeredstructure, a lower layer (or a first layer) abutting on the emitterregion 121 or the back surface field regions 172 may be formed of nickel(Ni), a middle layer (or a second layer) on the lower layer may beformed of copper (Cu), and an upper layer (or a third layer) on themiddle layer may be formed of silver (Ag) or tin (Sn).

When at least one of the front electrode part 140 and the back electrodepart 150 formed using the plating method has the double-layeredstructure, a thickness of the lower layer may be about 0.5 μm to 1 μm,and a thickness of the upper layer may be about 5 μm to 10 μm. When atleast one of the front electrode part 140 and the back electrode part150 formed using the plating method has the triple-layered structure,each of the lower layer and the upper layer may have a thickness ofabout 0.5 μm to 1 μm, and a thickness of the middle layer may be about 5μm to 10 μm.

In this instance, the lower layer is to reduce a contact resistancebetween the lower layer and the emitter region 121 or the back surfacefield regions 172 abutting on the lower layer, and is to improve contactcharacteristics. The middle layer may be formed of a relativelyinexpensive material with good conductivity, for example, copper (Cu) inconsideration of cost reduction. If the middle layer is formed of copper(Cu), the lower layer underlying the middle layer may prevent copper(Cu), which is smoothly bonded to silicon (Si), from serving as animpurity region, which is penetrated (absorbed) in the emitter region121 or the back surface field regions 172 formed of silicon (Si) tothereby reduce or prevent the movement of carriers.

The upper layer prevents the oxidation of the layer (for example, thelower layer or the middle layer) underlying the upper layer and improvesan adhesive strength between the layer (for example, the lower layer orthe middle layer) and a conductive film, for example, a ribbonpositioned on the upper layer.

As described above, at least one of the front electrode part 140 and theback electrode part 150 formed using the plating method may have thedouble-layered structure or the triple-layered structure, and the lowerlayer may be formed of nickel (Ni). In this instance, nickel silicidecompounds exist between the lower layer and the emitter region 121 orbetween the lower layer and the back surface field regions 172 becauseof a bond between nickel (Ni) and silicon (Si) of the emitter region 121(i.e., the second conductive type region of the substrate 110) or a bondbetween nickel (Ni) and silicon (Si) of the back surface field regions172 (i.e., the heavily doped region of the substrate 110 doped withimpurities of the first conductive type).

Alternatively, at least one of the front electrode part 140 and the backelectrode part 150 may be formed through a screen printing method usingan Ag paste containing a glass fit or an Al paste containing the glassfrit. In this instance, the glass frit may pass through theanti-reflection layer 130 or the passivation layer 190 and may abut onthe emitter region 121 or the back surface field regions 172.

Accordingly, at least one of components of the glass frit is detected ina contact portion between the front electrode part 140 and the emitterregion 121 or a contact portion between the back electrode part 150 andthe back surface field regions 172. For example, at least one of lead(Pb)-based material such as PbO, bismuth (Bi)-based material such asBi₂O₃, aluminum (Al)-based material such as Al₂O₃, boron (B)-basedmaterial such as B₂O₃, tin (Sn)-based material, zinc (Zn)-based materialsuch as ZnO, titanium (Ti)-based material such as TiO, and phosphorus(P)-based material such as P₂O₅ contained in the glass frit may bedetected.

On the other hand, when at least one of the front electrode part 140 andthe back electrode part 150 is formed using the plating method, thecomponent of the glass fit is not detected between the substrate 110(i.e., the emitter region 121) and the front electrode part 140including the front electrodes 141 and the front bus bars 142 andbetween the substrate 110 (i.e., the back surface field regions 172) andthe back electrode part 150 including the back electrodes 151 and theback bus bars 152.

As described above, when at least one of the front electrode part 140and the back electrode part 150 has the multi-layered structure, thelower layer, the middle layer, and the upper layer are sequentiallyformed using the plating method to have a desired thickness.

In the embodiment of the invention, the number of front electrodes 141,the number of front bus bars 142, the number of back electrodes 151, andthe number of back bus bars 152 may vary, if desired or necessary.

Each front bus bar 142 and each back bus bar 152 respectively collectcarriers from the emitter region 121 and the back surface field regions172, and also respectively output carriers collected by the frontelectrodes 141 and carriers collected by the back electrodes 151 to theexternal device.

In another embodiment, at least one of the front bus bar 142 and theback bus bar 152 may be positioned directly on at least one of theanti-reflection layer 130 and the passivation layer 190 and may abut onat least one of the anti-reflection layer 130 and the passivation layer190.

As described above, because each of the front surface and the backsurface of the substrate 110 has the first and second textured surfaces,a surface area of the substrate 110 increases.

Hence, an area of the emitter region 121 contacting each front electrode141 and an area of the back surface field region 172 contacting eachback electrode 151 increase. Therefore, even if a width W11 of eachfront electrode 141 and a width W12 of each back electrode 151 decrease,a contact area between the emitter region 121 and the front electrode141 and a contact area between the back surface field region 172 and theback electrode 151 may not decrease.

As a result, even if the width W11 of each front electrode 141 and thewidth W12 of each back electrode 151 decrease, an amount of carriersmoving from the emitter region 121 to the front electrodes 141 and anamount of carriers moving from the back surface field regions 172 to theback electrodes 151 may not decrease.

In the embodiment of the invention, the width W11 of each frontelectrode 141 and the width W12 of each back electrode 151 may be about40 μm to 50 μm. The widths W11 and W12 are much less than a width (ofabout 60 μm to 100 μm) of electrodes of a comparative example.

As described above, because formation areas of the front electrodes 141and the back electrodes 151 to prevent or reduce the incidence of lightat the front surface and the back surface of the substrate 110 arereduced, an amount of light incident on the front surface and the backsurface of the substrate 110 increases.

However, a moving distance of carriers moving to the front electrodes141 along the emitter region 121 and a moving distance of carriersmoving to the back electrodes 151 along the back surface field regions172 increase because of the first and second textured surfaces of thesubstrate 110.

Accordingly, in the embodiment of the invention, a distance D11 betweenthe two adjacent front electrodes 141 and a distance D12 between the twoadjacent back electrodes 151 may decrease, so as to compensate for anincrease in the moving distance of carriers resulting from an increasein a surface area of the emitter region 121 and a surface area of theback surface field regions 172. For example, the distance D11 betweenthe two adjacent front electrodes 141 and the distance D12 between thetwo adjacent back electrodes 151 may be equal to or greater than about1.5 mm and less than about 2.0 mm.

As described above, because the width W11 of each front electrode 141and the width W12 of each back electrode 151 decrease, an incident areaof light at the front surface and the back surface of the substrate 110does not decrease even if the distances D11 and D12 increases.

An operation of the solar cell having the above-described structure isdescribed below.

When light irradiated to the solar cell is incident on the substrate 110and at least one of the emitter region 121 and the back surface fieldregion 172, each of which is the semiconductor part, through at leastone of the anti-reflection layer 130 and the passivation layer 190,electrons and holes are generated in the substrate 110 by light energyproduced based on the incident light. In this instance, because areflection loss of the light incident on the substrate 110 is reduced bythe first and second textured surfaces of the substrate 110, theanti-reflection layer 130, and the passivation layer 190, an amount oflight incident on the substrate 110 increases.

The electrons move to the n-type semiconductor part (for example, thesubstrate 110) and the holes move to the p-type semiconductor part (forexample, the emitter region 121) by the p-n junction of the substrate110 and the emitter region 121.

The holes moving to the emitter region 121 are collected by the frontelectrodes 141 and the front bus bars 142 and then move along the frontbus bars 142. The electrons moving to the substrate 110 pass through theback surface field regions 172, are collected by the back electrodes 151and the back bus bars 152, and move along the back bus bars 152. Whenthe front bus bars 142 are connected to the back bus bars 152 usingelectric wires such as a conductive film, current flows therein tothereby enable use of the current for electric power.

As described above, each of the front surface and the back surface ofthe substrate 110 has the double texturing structure including the firstprotrusions 11 having the size of several μm and the second protrusions111 having the size of several hundreds of nm, the incident area of thesubstrate 110 increases. Further, a reflection amount of light decreasesdue to a reflection operation using the first and second protrusions 11and 111, and an amount of light incident on the substrate 110 increases.

The efficiency of the solar cell is improved by the anti-reflectioneffect using the refractive indexes of the anti-reflection layer 130 andthe passivation layer 190, the field passivation effect using the fixedcharges, and the surface passivation effect using hydrogen (H) or oxygen(O).

A method for manufacturing the solar cell according to the embodiment ofthe invention is described below with reference to FIGS. 4A to 4H.

As shown in FIG. 4A, a wet etching process is performed on a frontsurface and a back surface of a substrate 110 of a first conductive type(for example, n-type) to form a first textured surface having aplurality of first protrusions 11 and a plurality of first depressions12.

The substrate 110 may be a crystalline semiconductor formed of singlecrystal silicon.

When the substrate 110 is formed of single crystal silicon, the firsttextured surface 11(12) may be formed using an alkali solution such asisopropyl alcohol (IPA) or potassium hydroxide (KOH).

Each of the first protrusions 11 may have a pyramid shape, such as atriangular pyramid. A diameter (i.e., size) and a protruding height ofeach first protrusion 11 may be about 5 μm to 10 μm.

Next, as shown in FIG. 4B, after the first textured surface 11(12) isformed, a second textured surface having a plurality of secondprotrusions 111 and a plurality of second depressions 112 is formed onthe surface of each first protrusion 11 using a dry etching method suchas a reaction ion etching (RIE) method.

A maximum diameter (i.e., size) and a protruding height of each secondprotrusion 111 may be about 300 nm to 600 nm.

In the embodiment of the invention, an etching gas used in the RIEmethod may be a mixture of SF₆ and Cl₂. Other gases may be used.

After the second textured surface 111(112) is formed, a process forremoving a remainder of the surface (or a portion of a surface layer) ofthe substrate 110 may be additionally performed. The remainder may beremoved using a dry gas (used in the dry etching method) of a processroom (or chamber) used to form the second textured surface 111(112),instead of the use of a separate process room (or chamber). In thisinstance, time required in the removing process of the remainder usingthe dry etching method is further reduced as compared to the wet etchingmethod.

Further, if the remainder is removed using the wet etching method, theuneven portions of the first and second textured surfaces may bedeformed. However, when the remainder is removed using the dry etchingmethod, the uneven portions of the first and second textured surfacesare not deformed, and thus changes or deviations in the reflectance oflight resulting from the first and second textured surfaces are notgenerated.

Next, as shown in FIG. 4C, ions (hereinafter, referred to as ‘firstimpurity ions’) of first impurities of a predetermined conductive typeare implanted into the front surface of the substrate 110 using an ionimplantation method.

In this instance, the predetermined conductive type may be a secondconductive type (for example, p-type) opposite the first conductive typeof the substrate 110. In the embodiment of the invention, the firstimpurities may use boron (B). Thus, the first impurity ions may bepositive ions B⁺ of boron (B).

More specifically, the first impurity ions of the second conductive typeare implanted into the exposed front surface of the substrate 110 toform an impurity region, i.e., a first impurity region 120 of the secondconductive type at the front surface of the substrate 110.

Subsequently, ions (hereinafter, referred to as ‘second impurity ions’)of second impurities of a predetermined conductive type (i.e., the firstconductive type) are implanted into the back surface of the substrate110 using the ion implantation method to form a second impurity region170 of the first conductive type at the back surface of the substrate110.

In the embodiment of the invention, the second impurities may usephosphorus (P). Thus, the second impurity ions may be positive ions P⁺of phosphorus (P).

A mask to implant the ions only into a desired region of each of thefront surface and the back surface of the substrate 110 may be used inthe ion implantation process for forming the first and second impurityregions 120 and 170.

For example, the mask positioned on the front surface of the substrate110 may block only an edge of the front surface of the substrate 110 andmay expose a remaining portion of the front surface of the substrate 110except the edge. Further, the mask positioned on the back surface of thesubstrate 110 may expose only a region to form a back surface fieldregion and may block a remaining portion of the back surface of thesubstrate 110.

Acceleration energy of ions for implanting the first and second impurityions into the substrate 110 may be about 1 keV to 20 keV. Animplantation depth of ions may be determined depending on theacceleration energy.

Thus, acceleration energy for the first impurity region 120 may bedifferent from acceleration energy for the second impurity region 170.For example, acceleration energy used to implant ions of p-typeimpurities into the substrate 110 may be greater than accelerationenergy used to implant ions of n-type impurities into the substrate 110.

In the embodiment of the invention, formation order of the firstimpurity region 120 and the second impurity region 170 may vary. Thefirst impurity region 120 and the second impurity region 170 may beformed in the same chamber or respective chambers.

Next, as shown in FIG. 4D, after the first and second impurity regions120 and 170 are formed, a thermal process is performed on the substrate110 having the first and second impurity regions 120 and 170 in anatmosphere of nitrogen (N₂) or oxygen (O₂). Thus, the first and secondimpurity regions 120 and 170 are completely activated. Hence, the firstimpurity region 120 forms an emitter region 121 positioned at the frontsurface of the substrate 110, and thus the emitter region 121 and thesubstrate 110 form a p-n junction. Further, the second impurity region170 forms a plurality of back surface field regions 172 positioned atthe back surface of the substrate 110.

In other words, an implantation state of the p-type and n-type impurityions of the first and second impurity regions 120 and 170 changes froman interstitial state to a substitutional state because of theactivation of the first and second impurity regions 120 and 170 throughthe thermal process. Hence, silicon and the p-type and n-type impurityions are rearranged. As a result, the first and second impurity regions120 and 170 respectively serve as the p-type emitter region 121 and then-type back surface field regions 172.

Solubility of boron (B) used to form the emitter region 121 is less thansolubility of phosphorus (P) used to form the back surface field regions172. Therefore, an activation temperature of the first and secondimpurity regions 120 and 170 is determined based on the first impurityregion 120, so as to stably activate the first impurity region 120.

The activation temperature of the first and second impurity regions 120and 170 may be about 1,000° C. to 2,000° C., and time required in thethermal process may be about 20 minutes to 60 minutes.

In the embodiment of the invention, because the activation process isperformed at a high temperature equal to or higher than about 1,000° C.capable of stably activating boron (B), the first impurity region 120 aswell as the second impurity region 170 are stably activated. Hence, theemitter region 121 and the back surface field regions 172 are smoothlyformed.

Furthermore, because the thermal process is performed at the hightemperature equal to or higher than about 1,000° C., a damaged portiongenerated in the ion implantation process for the first and secondimpurity regions 120 and 170 is recrystallized. Hence, the damagedportion generated in the ion implantation process is recovered without aseparate damage removal process using the wet etching method, etc.

When the second textured surface 111(112) is formed using the RIEmethod, a damaged portion of the surface of the substrate 110 isgenerated because of plasma generated in the process. However, asdescribed above, the damaged portion is recovered by therecrystallization of silicon (S1) through the thermal process performedat the high temperature equal to or higher than about 1,000° C.Therefore, a separate damage removal process using the wet etchingmethod, etc., is not necessary.

Because of these reasons, the removing process of the remainder, whichmay be performed after the formation of the first and second texturedsurfaces, may be omitted.

In the embodiment of the invention, the damaged portion, which is formedin the surface of the substrate 110 (or the emitter region 121) in theRIE process and the ion implantation process, is recovered by theactivation process of the first impurity region 120 at the hightemperature (equal to or higher than about 1,000° C.) for the p-typeemitter region 121. Hence, the reflectance of light of a shortwavelength band incident on the emitter region 121 does not increase.

Next, as shown in FIG. 4E, a first passivation layer 191 formed ofhydrogenated silicon nitride (SiNx:H) is formed on the back surface ofthe substrate 110. The first passivation layer 191 may be formed using adeposition method such as a plasma enhanced chemical vapor deposition(PECVD) method. In the embodiment of the invention, the firstpassivation layer 191 may have a thickness of about 70 nm to 100 nm.

Next, as shown in FIG. 4F, layers formed of aluminum oxide (Al₂O₃) arerespectively formed on the emitter region 121 positioned at the frontsurface of the substrate 110 and the first passivation layer 191positioned on the back surface of the substrate 110 to form a firstanti-reflection layer 131 on the emitter region 121 and a secondpassivation layer 192 on the first passivation layer 191.

The aluminum oxide layers may be formed using the PECVD method, anatomic layer deposition (ALD) method, etc.

When the aluminum oxide layer is formed using the PECVD method, thelayer is stacked only in a portion exposed by a process gas. Therefore,the first anti-reflection layer 131 and the second passivation layer192, each of which is formed of aluminum oxide, are respectively formedon the front surface and the back surface of the substrate 110 throughthe separate PECVD method.

In this instance, the first anti-reflection layer 131 and the secondpassivation layer 192 respectively positioned on the front surface andthe back surface of the substrate 110 may be formed under the sameprocess conditions to thereby have the same characteristics.Alternatively, the first anti-reflection layer 131 and the secondpassivation layer 192 may be formed under different process conditionsto thereby have different characteristics.

However, when the aluminum oxide layers are formed using the ALD method,the aluminum oxide layers may be formed on the front surface, the backsurface, and the lateral surface of the substrate 110 through onestacking process. Thus, the aluminum oxide layers are simultaneouslyformed on the front surface and the back surface of the substrate 110through one ALD process to form the first anti-reflection layer 131 andthe second passivation layer 192.

Because the first anti-reflection layer 131 and the second passivationlayer 192 respectively positioned on the front surface and the backsurface of the substrate 110 are formed under the same processconditions, the first anti-reflection layer 131 and the secondpassivation layer 192 have the same characteristics.

In the embodiment of the invention, the first anti-reflection layer 131and the second passivation layer 192 may have a thickness of about 5 nmto 15 nm.

Hence, a passivation layer 190 including the first and secondpassivation layers 191 and 192 is formed on the back surface of thesubstrate 110.

Next, as shown in FIG. 4G, a second anti-reflection layer 132 formed ofhydrogenated silicon nitride (SiNx:H) is formed on the firstanti-reflection layer 131 using the PECVD method at a thickness of about70 nm to 100 nm. Hence, an anti-reflection layer 130 including the firstand second anti-reflection layers 131 and 132 is formed.

As described above, the anti-reflection layer 130 including the firstanti-reflection layer 131 formed of aluminum oxide (Al₂O₃) and thesecond anti-reflection layer 132 formed of hydrogenated silicon nitride(SiNx:H) is formed on the front surface of the substrate 110, and thepassivation layer 190 including the first passivation layer 191 formedof hydrogenated silicon nitride (SiNx:H) and the second passivationlayer 192 formed of aluminum oxide (Al₂O₃) is formed on the back surfaceof the substrate 110. Afterward, a front electrode part 140 including aplurality of front electrodes 141 and a plurality of front bus bars 142,which pass through the anti-reflection layer 130 and abut on the emitterregion 121 underlying the anti-reflection layer 130, is formed. Further,a back electrode part 150 including a plurality of back electrodes 151and a plurality of back bus bars 152, which pass through the passivationlayer 190 and abut on the back surface field regions 172 underlying thepassivation layer 190, is formed. As a result, the solar cell shown inFIGS. 1 and 2 is completed.

An example of a method for forming the front electrode part 140 and theback electrode part 150 is described with reference to FIG. 4H.

For example, as shown in FIG. 4H, a laser beam is selectively irradiatedonto each of the front surface and the back surface of the substrate 110to form a plurality of first and second openings 181 and 182 at alocation to form the front electrode part 140 and the back electrodepart 150.

The plurality of first openings 181 pass through the anti-reflectionlayer 130 and expose the emitter region 121 underlying the openedportions of the anti-reflection layer 130. The plurality of secondopenings 182 pass through the passivation layer 190 and expose the backsurface field regions 172 underlying the opened portions of thepassivation layer 190.

The plurality of first openings 181 are used to form the plurality offront electrodes 141 and the plurality of front bus bars 142. In thisinstance, a width of the first opening 181 for each front electrode 141is less than a width of the first opening 181 for each front bus bar142.

The plurality of second openings 182 are used to form the plurality ofback electrodes 151 and the plurality of back bus bars 152. In thisinstance, a width of the second opening 182 for each back electrode 151is less than a width of the second opening 182 for each back bus bar152.

The number of first openings 181 for the front electrodes 141 may beless than the number of second openings 182 for the back electrodes 151.Hence, a distance between the two adjacent first openings 181 may begreater than a distance between the two adjacent second openings 182.

The first openings 181 for the front bus bars 142 may be positionedopposite the second openings 182 for the back bus bars 152 with thesubstrate 110 between them.

Subsequently, the front electrode part 140 and the back electrode part150 are respectively formed on the emitter region 121 and the backsurface field regions 172 exposed by the first and second openings 181and 182 using an electroplating method or an electroless plating method.

In another embodiment, the front electrodes 141, the front bus bars 142,the back electrodes 151, and the back bus bars 152 may be formed bycoating a metal paste containing a metal material such as silver (Ag) onthe first and second openings 181 and 182 using a screen printingmethod, etc., and then performing a thermal process on the metal pasteat a desired temperature.

In another embodiment, the front electrodes 141, the front bus bars 142,the back electrodes 151, and the back bus bars 152 may be formed bycoating and drying a metal paste containing at least one of silver (Ag)and aluminum (Al) on the anti-reflection layer 130 and the passivationlayer 190 and then performing a thermal process on the metal paste.Hence, the front electrode part 140 including the front electrodes 141and the front bus bars 142 may be formed on the emitter region 121, andthe back electrode part 150 including the back electrodes 151 and theback bus bars 152 may be formed on the back surface field regions 172.

Because the front electrode part 140 and the back electrode part 150have to partially pass through the anti-reflection layer 130 and thepassivation layer 190, respectively, the metal paste may contain anetchant, for example, PbO for etching the anti-reflection layer 130 andthe passivation layer 190. An amount and a kind of the etchant containedin the metal paste may be determined depending on a thickness or amaterial of the anti-reflection layer 130 and the passivation layer 190.

When the thermal process is performed on the metal paste coated on theanti-reflection layer 130 and the passivation layer 190, the metal pastepasses through the anti-reflection layer 130 and the passivation layer190 and is chemically bonded to the emitter region 121 and the backsurface field regions 172 underlying the anti-reflection layer 130 andthe passivation layer 190. Hence, the front electrode part 140electrically and physically connected to the emitter region 121 and theback electrode part 150 electrically and physically connected to theback surface field regions 172 are formed.

When at least one of the anti-reflection layer 130 and the passivationlayer 190 is omitted, at least one of the front electrode part 140 andthe back electrode part 150 may not contain the etchant because it doesnot need to pass through the omitted component (i.e., at least one ofthe anti-reflection layer 130 and the passivation layer 190).

When at least one of the front bus bar 142 and the back bus bar 152 ispositioned directly on the anti-reflection layer 130 or the passivationlayer 190, at least one of the front bus bar 142 and the back bus bar152 may not contain the etchant because it does not need to pass throughthe anti-reflection layer 130 or the passivation layer 190.Alternatively, at least one of the front bus bar 142 and the back busbar 152 may contain a small amount of the etchant which may not passthrough the anti-reflection layer 130 or the passivation layer 190.

In this instance, at least one of the front electrode 141, the front busbar 142, the back electrode 151, and the back bus bar 152 may be formedof a material different from other components.

Another example of a solar cell according to an example embodiment ofthe invention is described below with reference to FIG. 5.

Structures and components identical or equivalent to those described inthe solar cell shown in FIGS. 1 to 3 are designated with the samereference numerals, and a further description may be briefly made or maybe entirely omitted.

Unlike the solar cell shown in FIGS. 1 and 2, a solar cell shown in FIG.5 further includes hydrogenated silicon oxide (SiOx:H) layers onhydrogenated silicon nitride (SiNx:H) layers respectively positioned ona front surface and a back surface of a substrate 110.

More specifically, an anti-reflection layer 130 a positioned on thefront surface of the substrate 110 further includes a thirdanti-reflection layer 133, which is positioned directly on a secondanti-reflection layer 132 and is formed of hydrogenated silicon oxide(SiOx:H), in addition to a first anti-reflection layer 131 formed ofaluminum oxide (Al₂O₃) and the second anti-reflection layer 132 formedof hydrogenated silicon nitride (SiNx:H). Hence, the anti-reflectionlayer 130 a has a triple-layered structure including the layers 131 to133.

Further, a passivation layer 190 a positioned on the back surface of thesubstrate 110 includes a first passivation layer 191 formed ofhydrogenated silicon nitride (SiNx:H), a second passivation layer 192 a,which is positioned directly on the first passivation layer 191 and isformed of hydrogenated silicon oxide (SiOx:H), and a third passivationlayer 193, which is positioned directly on the second passivation layer192 a and is formed of aluminum oxide (Al₂O₃).

In other words, the solar cell shown in FIG. 5 further includes thehydrogenated silicon oxide layer between the hydrogenated siliconnitride layer and the aluminum oxide layer, unlike the solar cell shownin FIGS. 1 and 2. Thus, the passivation layer 190 a has a triple-layeredstructure including the layers 191, 192 a, and 193.

As described above, the hydrogenated silicon oxide layers 133 and 192 apositioned directly on the hydrogenated silicon nitride layers 132 and191 prevent hydrogen (H), which is contained in the hydrogenated siliconnitride layers 132 and 191 and performs a surface passivation function,from moving in a direction opposite the substrate 110. Thus, thehydrogenated silicon oxide layers 133 and 192 a included in theanti-reflection layer 130 a and the passivation layer 190 a serve ascapping layers of the hydrogenated silicon nitride layers 132 and 191underlying the hydrogenated silicon oxide layers 133 and 192 a.

The hydrogenated silicon oxide layers 133 and 192 a contain hydrogen (H)capable of recovering a defect. Hence, hydrogen (H) contained in thehydrogenated silicon oxide layers 133 and 192 a moves to the surface ofthe substrate 110 and performs the surface passivation function.

Accordingly, a surface passivation effect is further improved by thehydrogenated silicon oxide layers 133 and 192 a respectively positionedon the front surface and the back surface of the substrate 110.

The hydrogenated silicon oxide layers 133 and 192 a are formed using aPECVD method. Unlike the formation order of the anti-reflection layer130 and the passivation layer 190 in the solar cell shown in FIGS. 1 and2, the anti-reflection layer 130 a and the passivation layer 190 a areformed in the following formation order.

For example, after the first passivation layer 191 formed ofhydrogenated silicon nitride (SiNx:H) is formed on the back surface ofthe substrate 110 using the PECVD method, the second passivation layer192 a formed of hydrogenated silicon oxide (SiOx:H) is formed on thefirst passivation layer 191 using the PECVD method. Then, the thirdpassivation layer 193 and the first anti-reflection layer 131, each ofwhich is formed of aluminum oxide (Al₂O₃), are simultaneously formed onthe second passivation layer 192 a and the emitter region 121 positionedat the front surface of the substrate 110 using an ALD method,respectively. Then, the second anti-reflection layer 132 formed ofhydrogenated silicon nitride (SiNx:H) and the third anti-reflectionlayer 133 formed of hydrogenated silicon oxide (SiOx:H) are sequentiallyformed on the first anti-reflection layer 131 positioned on the frontsurface of the substrate 110 using the PECVD method.

The solar cell shown in FIG. 5 is manufactured through the manufacturingprocesses illustrated in FIGS. 4A to 4F, except the formation method andthe formation order of the anti-reflection layer 130 a and thepassivation layer 190 a.

The third anti-reflection layer 133 and the second passivation layer 192a, each of which is formed of hydrogenated silicon oxide (SiOx:H) mayhave a thickness of about 50 nm to 100 nm and a refractive index ofabout 1.5.

As described above, the second anti-reflection layer 132 and the firstpassivation layer 191 formed of hydrogenated silicon nitride (SiNx:H)are respectively capped by the third anti-reflection layer 133 and thesecond passivation layer 192 a formed of hydrogenated silicon oxide(SiOx:H). Hence, the passivation function performed by the secondanti-reflection layer 132 and the first passivation layer 191 is furtherimproved. Further, the passivation effect of the solar cell shown inFIG. 5 is further improved because of the passivation function performedby the third anti-reflection layer 133 and the second passivation layer192 a.

Because the anti-reflection layer 130 a and the passivation layer 190 afurther include the third anti-reflection layer 133 and the secondpassivation layer 192 a formed of hydrogenated silicon oxide (SiOx:H),the anti-reflection effect at the front surface and the back surface ofthe substrate 110 is improved. Hence, an amount of light incident on thesubstrate 110 increases, and an amount of electric current output fromthe solar cell increases.

Other examples of the solar cell shown in FIGS. 1 to 3 and the solarcell shown in FIG. 5 are described below with reference to FIGS. 6 and7.

FIG. 6 illustrates another example of the solar cell shown in FIGS. 1 to3, and FIG. 7 illustrates another example of the solar cell shown inFIG. 5.

The solar cells shown in FIGS. 6 and 7 further include a silicon oxide(SiOx) layer 180 between an emitter region 121 and an anti-reflectionlayer 130 (130 a) and between a back surface of a substrate 110 and afirst passivation layer 191, unlike the solar cell shown in FIGS. 1 to 3and the solar cell shown in FIG. 5.

The solar cells shown in FIGS. 6 and 7 substantially have the sameconfiguration as the solar cell shown in FIGS. 1 to 3 and the solar cellshown in FIG. 5, except the silicon oxide layer 180, respectively.

As shown in FIGS. 6 and 7, the silicon oxide layer 180 is positioneddirectly on the emitter region 121 positioned at a front surface of thesubstrate 110 and directly on the back surface of the substrate 110. Theanti-reflection layer 130 (130 a) and a passivation layer 190 (190 a)are positioned directly on the silicon oxide layer 180.

The silicon oxide layer 180 is an oxide layer deliberately formed byimmersing the substrate 110 in a desired chemical solution. A thicknessof the silicon oxide layer 180 may be about 2 nm to 3 nm.

In the method for manufacturing the solar cell illustrated in FIGS. 4Ato 4F, after the emitter region 121 is formed, the silicon oxide layer180 is formed before forming the anti-reflection layer 130 and thepassivation layer 190.

The silicon oxide layer 180 is formed by immersing the substrate 110 ina nitric acid (NHO₃) solution having a hydrogen ion concentration (pH)of about 2 to 4 at a process temperature of the normal temperature toabout 70° C. for about 5 minutes to 30 minutes. A concentration of NHO₃in the NHO₃ solution, i.e., an amount of NHO₃ in the NHO₃ solution maybe about 65% to 70%.

In the process for forming the anti-reflection layer 130 (130 a) and thepassivation layer 190 (190 a) on the emitter region 121 and the backsurface field regions 172, a natural oxide layer generated by oxygenexisting in the atmosphere or the process room is generally formeddirectly on the emitter region 121. The natural oxide layer formed thusis unstably bonded to silicon existing in the substrate 110 or theemitter region 121, thereby generating a defect. In embodiments of theinvention, the natural oxide layer is one that is formed spontaneouslyand unintentionally.

When the layer such as the aluminum oxide (Al₂O₃) layer is formed on thenatural oxide layer, water (H₂O) is generated by the bond betweenhydrogen (H) contained in a process material for the layer formation andthe natural oxide layer having the unstable bond. Further, a blisteringphenomenon such as a spot resulting from the formation of a hydrogenmolecule is generated.

However, in the embodiment of the invention, the silicon oxide layer 180having the characteristics better than the natural oxide layer is formeddirectly on each of the front surface and the back surface of thesubstrate 110 using the separate PECVD method. Therefore, the frequencyof problem generated by a bond of hydrogen and oxygen is greatlyreduced.

Oxygen contained in the silicon oxide layer 180 performs the passivationfunction for converting the bonds existing at the surface of thesubstrate 110 into stable bonds, thereby further improving the surfacepassivation effect.

As shown in FIGS. 6 and 7, the silicon oxide layer 180 is formed on boththe front surface and the back surface of the substrate 110. In anotherembodiment, the silicon oxide layer 180 may be formed on only one of thefront surface and the back surface of the substrate 110.

As described above, the silicon oxide layer 180 is formed so as toimprove the surface passivation effect at the front surface and the backsurface of the substrate 110 and to reduce the problem resulting fromthe natural oxide layer. Therefore, the silicon oxide layer 180 is notrequired to be thick and may have a thickness of about 2 nm to 3 nm.

The embodiment of the invention was described based on a bifacial solarcell, in which light is incident on both the front surface and the backsurface of the substrate 110. The embodiment of the invention may beapplied to other kinds of solar cells, for example, other kinds of solarcells using n-type single crystal silicon.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the scope of the principles of thisdisclosure. More particularly, various variations and modifications arepossible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

What is claimed is:
 1. A solar cell comprising: a substrate formed of ann-type crystalline semiconductor; an emitter region of a p-typepositioned at a first surface of the substrate; an anti-reflection layerpositioned on the first surface of the substrate; a passivation layerpositioned on a second surface which is opposite of the first surface ofthe substrate; a first electrode which is positioned on the firstsurface of the substrate and is connected to the emitter region; and asecond electrode which is positioned on the second surface of thesubstrate and is connected to the substrate, wherein the anti-reflectionlayer includes a first anti-reflection layer formed of aluminum oxide, asecond anti-reflection layer which is positioned directly on the firstanti-reflection layer and is formed of hydrogenated silicon nitride, anda third anti-reflection layer which is positioned directly on the secondanti-reflection layer and is formed of hydrogenated silicon oxide,wherein the passivation layer includes a first passivation layer formedof hydrogenated silicon nitride, a second passivation layer which ispositioned directly on the first passivation layer and is foamed ofhydrogenated silicon oxide, and a third passivation layer which ispositioned directly on the second passivation layer and is formed ofaluminum oxide, wherein the emitter region has a first textured surfaceincluding a plurality of first protrusions each having a protrudingheight and a maximum diameter which are within a range of about 5 μm to10 μm, and wherein each of the plurality of first protrusions has asecond textured surface including a plurality of second protrusions eachhaving a protruding height and a maximum diameter which are within arange of about 300 nm to 600 nm.
 2. The solar cell of claim 1, whereinthe first anti-reflection layer has a thickness of about 5 nm to 15 nm.3. The solar cell of claim 2, wherein each of the second anti-reflectionlayer and the first passivation layer has a thickness of about 70 nm to100 nm.
 4. The solar cell of claim 1, wherein the second passivationlayer has a thickness of about 50 nm to 100 nm.
 5. The solar cell ofclaim 1, further comprising a silicon oxide layer positioned between thesecond surface of the substrate and the first passivation layer.
 6. Thesolar cell of claim 5, wherein the silicon oxide layer has a thicknessof about 2 nm to 3 nm.
 7. The solar cell of claim 1, wherein the firstsurface and the second surface of the substrate are incident surfaces onwhich light is incident.
 8. The solar cell of claim 1, wherein thehydrogenated silicon oxide of the third anti-reflective layer and thesecond passivation layer each has a thickness of about 50 nm to 100 nm.9. The solar cell of claim 1, further comprising a silicon oxide layerpositioned between the emitter region and the first anti-reflectionlayer.
 10. The solar cell of claim 9, wherein the silicon oxide layerhas a thickness of about 2 nm to 3 nm.
 11. The solar cell of claim 1,wherein acicular ends of the plurality of second protrusions point in aparallel direction as vertices of the plurality of first protrusions.12. The solar cell of claim 1, wherein the first and second texturedsurfaces are also formed on the second surface of the substrate.
 13. Thesolar cell of claim 1, wherein each of the plurality of secondprotrusions has an acicular end, and acicular ends of adjacent secondprotrusions are connected by serrated edges.